An observational study of extremely low birth weight babies looked at the association between acidemia, hypercapnia and severe intraventricular hemorrhage. Rates of severe IVH were higher in infants with a high base deficit (defined as a median base deficit of > 4 mEq/L) than in infants with a base deficit of < 4 mEq/L (16% vs 9%). In a multivariate analysis, adjusted risk for severe IVH increased with higher PaCO2 and higher base deficit. However arterial pH was the sole predictor of severe IVH. This suggests that In ELBW infants during the first 48 hours of life, the risk of IVH is higher with acidemia, rather than with hypercapnia per se.